The present invention provides a floating gate type EEPROM which employs a CVD insulator film as a tunnel oxide film through which electric charge is transferred between a floating gate electrode and another electrode, thereby enabling larger number of times of writing and erasing operations than that in the case of a conventional floating gate type EEPROM which employs a thermally oxidized film as the tunnel oxide film.
1. Field of the Invention
The present invention relates to an electrically erasable and programmable floating gate type non-volatile semiconductor memory which enables electrical writing and erasing operation to be readily effected.
2. Description of the Prior Art
The prior art shows at least, a floating gate type EEPROM, for example, the following patent U.S. Pat. No. 4,203,158 - Dov. Frohman-Bentchkowsky. et al. -May 13, 1980.
FIG. 2 is a sectional view of a conventional floating gate type EEPROM. On the surface of the P-type semiconductor substrate 11, there are provided the N.sup.+ type source area 12 and the drain area 13, above which is provided the oxidized gate film 14. In the small are adjacent to the drain area 13, there is provided the thin oxidized film 15, above which are provided the floating gate electrode 16, the second oxidized gate film 17 and the control gate electrode 18. Writing operation is conducted by applying a writing voltage to the control gate electrode 18, so that the electrons are injected from the drain area 13 into the floating gate electrode 16 through the thin oxidized film 15. Erasing operation is conducted by applying an erasing voltage to the control gate electrode 18, so that the electrons are extracted from the floating gate electrode 16 into the drain area 13 through the thin oxidized film 15. Writing and erasing operations in the floating gate type EEPROM are effected by means of Fowler-Nordheim tunnel current flowing through a thin oxide film (100 to 150.ANG.). This thin oxide film for writing and erasing operations has heretofore been constituted by a thermally oxidized film.
The thermally oxidized film 15 conventionally employed for writing and erasing has, however, the disadvantage that breakdown occurs when the number of times of writing and erasing operations reaches about 10.sup.4.